1. Field of the Invention
The present invention relates to a driving circuit for improving display quality of an LCD, and more particularly, to a driving circuit of a WOA (wiring on array) LCD device.
2. Description of the Prior Art
Liquid crystal displays, characterized by small size, low power consumption, and no radiation, have been broadly applied in portable information products such as notebook and PDA. It is likely that LCDs will replace CRT monitors in many settings.
In the driving circuit of LCDs of the prior art, the driving IC chips are packaged on the surface of a plurality of tape carrier packages (TCPs).
The TCPs are then electrically connected to a printed circuit board and a bottom glass substrate so as to ensure that the controlling signal from the printed circuit board can be sent to each driving IC chip via the TCPs, and thereafter be sent to the bottom glass substrate. Further, because of the high cost of the material, packaging, and testing of TCPs, a COG (chip on glass) or WOA (wiring on array) LCD is developed to reduce manufacturing cost and to increase product reliability.
Please refer to FIG. 1. As shown in FIG. 1, an LCD device, which adopts the COG or WOA design in a side (usually the scan line circuit side), comprises an LCD panel 10 and a first driving circuit for driving the LCD panel 10. The LCD panel is composed of a top glass substrate 12 and a bottom glass substrate 14. The first driving circuit comprises a plurality of driving IC chips 16 respectively packed on tape carrier packages (TCPs) 17 and electrically connected to the bottom glass substrate. The TCPs 17 are also electrically connected to the printed circuit board 20.
The LCD includes a second driving circuit comprising a bus line 22 installed on the surface of the bottom glass substrate 14. The second driving circuit also comprises a plurality of driving IC chips 18 installed on the surface of the bottom glass substrate and above the bus line 22 by employing chip-on-glass (COG) method. Each driving IC chip 18 comprises a plurality of input pads (not shown) for electrically connecting to the bus line 22, and each driving IC chip 18 is serially connected to the bus line 22.
The resistance of the conductive wire of the bus line 22 (for electrically connecting to the driving IC chips) formed on the surface of the bottom glass substrate is very large, therefore when a driving voltage of a controlling signal is sent from the printed circuit board 20, through the TCPs 17, the bus line 22, and to each driving IC chip 18, each driving IC chip would have a different voltage drop according to the position. This causes an evident diversity in the color, brightness, and contrast performance if the display color is sensitive (such as gray) when the driving IC chips 18 drive the LCD panel 10. In other words, the voltage drop inequality as a result of the resistance of the bus line 22 will make the equally inputted voltage decrease progressively so as to the display quality deteriorates.